Method and apparatus for providing force feedback to the user of an interactive computer simulation

ABSTRACT

An apparatus for interfacing the movement of a shaft with a computer includes a support, a gimbal mechanism having two degrees of freedom, and three electromechanical transducers. When a shaft is engaged with the gimbal mechanism, it can move with three degrees of freedom in a spherical coordinate space, where each degree of freedom is sensed by one of the three transducers. A fourth transducer can be used to sense rotation of the shaft around an axis. The method includes the steps of defining an origin in 3-dimensional space, physically constraining a shaft in the 3-dimensional space such that a portion of the shaft always intersects the origin and such that a portion of the shaft extending beyond the origin defines a radius in a spherical coordinate system, transducing a first electrical signal related to a first angular coordinate of the radius with a first transducer, transducing a second electrical signal related to a second angular coordinate with a second transducer, transducing a third electrical signal related to the length of the radius with a third transducer, and coupling the transducers to a computer.

This is a continuation application of prior application Ser. No. 08/275,120 filed on Jul. 14, 1994, U.S. Pat. No. 5623582.

BACKGROUND OF THE INVENTION

This invention relates generally to human/computer interface devices, and more particularly to computer input devices such as mice, trackballs, etc.

Virtual reality computer systems provide users with the illusion that they are part of a "virtual" environment. A virtual reality system will typically include a personal computer or workstation, specialized virtual reality software, and virtual reality I/O devices such as head mounted displays, pointer gloves, 3D pointers, etc.

For example, a virtual reality computer system can allow a doctor-trainee or other human operator or user to "manipulate" a scalpel or probe within a computer-simulated "body", and thereby perform medical procedures on a virtual patient. In this instance, the I/O device is typically a 3D pointer, stylus, or the like. As the "scalpel" or "probe" moves within the body image displayed on the screen of the computer system, results of such movement are updated and displayed so that the operator can gain the experience of such a procedure without practicing on an actual human being or a cadaver.

For virtual reality systems to provide a realistic (and therefore effective) experience for the user, sensory feedback and manual interaction should be as natural as possible. As virtual reality systems become more powerful and as the number of potential applications increases, there is a growing need for specific human/computer interface devices which allow users to interface with computer simulations with tools that realistically emulate the activities being represented within the virtual simulation. Such procedures as laparoscopic surgery, catheter insertion, and epidural analgesia should be realistically simulated with suitable human/computer interface devices if the doctor is to be properly trained.

While the state of the art in virtual simulation and medical imaging provides a rich and realistic visual feedback, there is a great need for new human/computer interface tools which allow users to perform natural manual interactions with the computer simulation. For medical simulation, there is a strong need to provide doctors with a realistic mechanism for performing the manual activities associated with medical procedures while allowing a computer to accurately keep track of their actions.

There are number of devices that are commercially available for interfacing a human with a computer for virtual reality simulations. There are, for example, such 2-dimensional input devices such as mice, trackballs, and digitizing tablets. However, 2-dimensional input devices tend to be awkward and inadequate to the task of interfacing with 3-dimensional virtual reality simulations. In contrast, a 3-dimensional human/computer interface tool sold under the trademark Immersion PROBE™ is marketed by Immersion Human Interface Corporation of Palo Alto, Calif., and allows manual control in 3-dimensional virtual reality computer environments. A pen-like stylus allows for dexterous 3-dimensional manipulation, and the position and orientation of the stylus is communicated to a host computer. The Immersion PROBE has six degrees of freedom which convey spatial coordinates (x, y, z) and orientation (role, pitch, yaw) of the stylus to the host computer.

While the Immersion PROBE is an excellent 3-dimensional interface tool, it may be inappropriate for certain virtual reality simulation applications. For example, in some of the aforementioned medical simulations three or four degrees of freedom of a 3-dimensional human/computer interface tool is sufficient and, often, more desirable than five or six degrees of freedom because it more accurately mimics the real-life constraints of the actual medical procedure. Therefore, a less complex, more compact, lighter weight, lower inertia and less expensive alternative to six degree of freedom human/computer interface tool is desirable for certain applications.

SUMMARY OF THE INVENTION

The present invention provides a 3-dimensional human/computer interface tool which is particularly well adapted to virtual reality simulation systems that require fewer degrees of freedom, e.g. two, three, or four degrees of freedom. The present invention therefore tends to be less complex, more compact, lighter weight, less expensive, more reliable and have less inertia than 3-dimensional human/computer interface tools of the prior art having more degrees of freedom.

The present invention is directed to a method and apparatus for providing an interface between a human and a computer. The human end of the interface is preferably a substantially cylindrical object such as a shaft of a surgeon's tool, a catheter, a wire, etc. Alternatively, it can comprise a pool cue, a screw driver shaft, or any other elongated object that is manipulated in 3-dimensional space by a human operator. In certain embodiments of the present invention, the computer develops signals to provide force feedback to the object. For example, a twisting or resisting force can be imparted on the object to provide haptic or force feedback of a medical procedure being performed in a virtual reality simulation.

An apparatus for interfacing with a electrical system includes a support, a gimbal mechanism coupled to the support, and preferably three electromechanical transducers, although certain embodiments (e.g. for use with catheters) may require only two electromechanical transducers. The gimbal mechanism has a base portion which is rotatably coupled to the support to provide a first degree of freedom, and an object receiving portion rotatably coupled to the base portion to provide a second degree of freedom. A first electromechanical transducer is coupled between the support and the base portion, a second electromechanical transducer is coupled between the base portion and the object receiving portion, and a third electromechanical transducer is coupled between the object receiving portion and an intermediate portion of an elongated object that is at least partially disposed within the object receiving portion. The third electromechanical transducer is associated with a third degree of freedom. Therefore, each of the three transducers are associated with a. degree of freedom of movement of the object when it is engaged with the object receiving portion of the gimbal mechanism.

More specifically, an apparatus for interfacing an operator manipulable shaft with a computer includes a support, a gimbal mechanism, and four sensors. The gimbal mechanism preferably includes a U shaped base portion having a base and a pair of substantially parallel legs extending therefrom, where the base of the U shaped base portion is rotatably coupled to the support, and a shaft receiving portion pivotally coupled between the legs of the base portion. The shaft receiving portion includes a translation interface and a rotation interface that engage the shaft when it is engaged with an aperture of the shaft receiving portion. The base portion rotates around a first axis and the shaft receiving portion rotates around a second axis substantially perpendicular to the first axis, such that an axis of the shaft defines a radius in a spherical coordinate system having an origin at an intersection of the first axis and the second axis. A first sensor is coupled between the support and the U shaped base portion to provide a first output signal, a second sensor is coupled between the U shaped base portion and the shaft receiving portion to produce a second output signal, a third sensor is coupled to the translation interface to produce a third output signal, and a fourth sensor is coupled between the rotation interface and the object to produce a fourth output signal. The output signals are preferably coupled to an input of a computer by an electronic interface.

In an alternative embodiment of the present invention a first actuator is coupled between the support and the U shaped base portion to produce a movement therebetween in response to a first input electrical signal, a second actuator is coupled between the U shaped base portion and the shaft receiving portion to produce a movement therebetween in response to a second input electrical signal, a third actuator is coupled to the translation interface to produce a mechanical movement of the elongated cylindrical object relative to the shaft receiving portion in response to a third input electrical signal, and a fourth actuator is coupled to the rotation interface to produce a mechanical movement of the elongated cylindrical object relative to the shaft receiving portion in response to a fourth input electrical signal.

A method for providing a human/computer interface includes the steps of: (a) defining an origin in a 3-dimensional space; (b) physically constraining a shaft that can be grasped by an operator such that a portion of the object always intersects the origin and such that the portion of the object extending past the origin defines a radius in a spherical coordinate system; (c) transducing a first electrical signal related to a first angular coordinate of the radius in the spherical coordinate system with a first transducer; (d) transducing a second electrical signal related to a second angular coordinate of the radius in the spherical coordinate system with a second transducer; (e) transducing a third electrical signal related to the length of the radius with a third transducer; and (f) electrically coupling the transducers to a computer system to provide a human/computer interface. The method can further include the step of transducing a fourth electrical signal related to a rotation of the shaft around an axis with a fourth transducer. The transducers are either sensors, actuators, or bi-directional transducers which can serve as either input or sensors.

It will therefore be appreciated that a human/computer interface of the present invention includes a support, a gimbal mechanism coupled to the support, and an elongated shaft engaged with the gimbal mechanism and having a grip area that can be grasped by a hand of an operator. The gimbal mechanism has a base portion rotatably coupled to the support, and a shaft receiving portion rotatably coupled to the base. A first sensor is coupled between the support and the base portion, a second sensor is coupled between the base portion and the shaft receiving portion, and a third sensor is coupled between the shaft receiving portion and an intermediate portion of the shaft. The three sensors are coupled to an input of a computer to provide the human/computer interface. Preferably, the interface further includes a fourth sensor coupled between the shaft receiving portion and an intermediate portion of the shaft, where the third sensor is a translation sensor and the fourth sensor is a rotation sensor.

The advantage of the present invention is that a 3-dimensional human/computer interface tool is provided which has the three or four degrees of freedom available that are desirable for many virtual reality simulation applications. The mechanism of the present invention is relatively straightforward allowing for low cost production and high reliability. Furthermore, since the human/computer interface tool of the present invention is constrained from movement along at certain degrees of freedom, it can more accurately simulate the use of tools and other elongated mechanical objects which are similarly constrained. Importantly, the present interface is of low inertia since the primary mass of the interface is located at the pivot point. This, along with the light weight of the interface, makes the interface less fatiguing to use.

In another embodiment of the present invention a human/computer interface tool is provided which is provided with only two degrees of freedom. This is particularly advantageous when the shaft is flexible, such as with very thin shafts, wires, catheters, and the like. With, for example, catheters, it is only necessary to provide two degrees of freedom (i.e. in-and-out, and rotation) and, therefore, sensors and/or actuators for the other degrees of freedom do not need to be provided.

These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a virtual reality system which employs an apparatus of the present invention to interface a laparoscopic tool handle with a computer system;

FIG. 2 is a perspective view of an apparatus for mechanically interfacing an elongated mechanical object with an electrical system in accordance with the present invention;

FIG. 2a is a perspective view of an alternative translation interface used for wires, catheters, and the like;

FIG. 3 is front elevation view of the apparatus of FIG. 2 illustrating a laparoscopic tool engaged with an object receiving portion of the present invention;

FIG. 4 is a side elevation similarly showing a laparoscopic tool engaged with the object receiving portion of the present invention;

FIG. 5 is a top plan view also illustrating the engagement of a laparoscopic tool with the object receiving portion of the present invention;

FIG. 6 is a pictorial view illustrating the four degrees of freedom enjoyed with the mechanism of the present invention;

FIG. 7 illustrates a first embodiment of an input sensor;

FIG. 8 illustrates a modified laparoscopic tool handle for the use of the present invention;

FIG. 8a is a cross-section taken along line 8a--8a of FIG. 8;

FIG. 9 is a perspective view of a sensor in accordance with the present invention;

FIG. 9a is a sectional view taken along line 9a--9a of FIG. 9.;

FIG. 9b is a perspective view of an alternative sensing wheel used for wires, catheters, and the like;

FIG. 10 is a perspective view of and alternative sensor mechanism of the present invention;

Figure 10a is a cross sectional view taken along line 10a--10a of FIG. 10;

FIG. 11 is a perspective view of another alternative sensor of the present invention; and

Figure 11a is a sectional view taken along line 11a--11a of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a virtual reality system 10 includes a human/computer interface apparatus 12, a electronic interface 14, and a computer 16. The illustrated virtual reality system 10 is directed to a virtual reality simulation of a laparoscopic surgery procedure. The software of the simulation is not a part of this invention and thus will not be discussed in any detail. However, such software is commercially available as, for example, Teleos™ from High Techsplanations of Rockville, Md. Suitable software drivers which interface such simulation software with computer input/output (I/O) devices are available from Immersion Human Interface Corporation of Palo Alto, Calif.

A laparoscopic tool 18 used in conjunction with the present invention is manipulated by an operator and virtual reality images are displayed on a screen 20 of the digital processing system in response to such manipulations. Preferably, the digital processing system is a personal computer or workstation, such as an IBM-PC AT or Macintosh personal computer, or a SUN or Silicon Graphics workstation. Most commonly, the digital processing system is a personal computer which operates under the MS-DOS operating system in conformance with an IBM PC AT standard.

The human/interface apparatus 12 as illustrated herein is used to simulate a laparoscopic medical procedure. In addition to a standard laparoscopic tool 18, the human/interface apparatus 12 includes a barrier 22 and a standard laparoscopic trocar 24. The barrier 22 is used to represent portion of the skin covering the body of a patient. Trocar 24 is inserted into the body of the patient to provide an entry and removal point from the body of the patient for the laparoscopic tool 18, and to allow the manipulation of the laparoscopic tool 18 within the body of the patient while minimizing tissue damage. Laparoscopic tools 18 and trocars 24 are commercially available from sources such as U.S. Surgical of Connecticut. Preferably, the laparoscopic tool 18 is modified such that the end of the tool (such as any cutting edges) are removed, leaving only the handle and the shaft. The end of the laparoscopic tool 18 is not required for the virtual reality simulation, and is removed to prevent any potential damage to persons or property. A gimbal apparatus 25 is shown within the "body"of the patient in phantom lines.

The laparoscopic tool 18 includes a handle or "grip" portion 26 and a shaft portion 28. The shaft portion is an elongated mechanical object and, in particular, is an elongated cylindrical object. The present invention is concerned with tracking the movement of the shaft portion 28 in three-dimensional space, where the movement has been constrained such that the shaft portion 28 has only three or four free degrees of motion. This is a good simulation of the real use of a laparoscopic tool 18 in that once it is inserted into a trocar 24 and through the gimbal apparatus 25, it is limited to about four degrees of freedom. More particularly, the shaft 28 is constrained at some point of along its length such that it can move with four degrees of freedom within the patient's body.

While the present invention will be discussed with reference to the shaft portion 28 of laparoscopic tool 18, it will be appreciated that a great number of other types of objects can be used with the method and apparatus of the present invention. In fact, the present invention can be used with any elongated mechanical object where is desirable to provide a human/computer interface with three or four degrees of freedom. Such objects may include catheters, hypodermic needles, wires, fiber optic bundles, screw drivers, pool cues, etc. Furthermore, although the described preferred embodiment of the present invention contemplates the use of a elongated cylindrical mechanical object, other embodiments of the present invention provide a similar human/computer interface for an elongated mechanical objects which are not cylindrical in shape.

The electronic interface 14 is a part of the human/computer interface apparatus 12 and coupled the apparatus 12 to the computer 16. An electronic interface 14 that is particularly well adopted for the present is described in U.S. patent application Ser. No. 08/092,974, filed Jul. 16, 1993 issued Nov. 19, 1996, as U.S. Pat. No. 5,576,727, and entitled "3-D Mechanical Mouse" assigned to the assignee of the present invention and incorporated herein by reference in its entirety. The electronic interface described therein was designed for the Immersion PROBE™ 3-D mechanical mouse and has six channels corresponding to the six degrees of freedom of the Immersion PROBE. However, in the context of the present invention, the electronic interface 14 requires the use of only four of the six channels, since the present invention is preferably constrained to no more than four degrees of freedom.

The electronic interface 14 is coupled to a gimbal apparatus 25 of the apparatus 12 by a cable 30 and is coupled to the computer 16 by a cable 32. In some embodiments of the present invention, interface 14 serves solely as an input device for the computer 16. In other embodiments of the present invention, interface 14 serves solely as an output device for the computer 16. In yet other embodiments of the present invention, the interface 14 serves as an input/output (I/O) device for the computer 16.

In an alternative embodiment of the present invention, interface 14 has a local microprocessor 33 preferably coupled with any transducers present in the interface 14 and with a transceiver 35. In such an embodiment, the computer 16 is coupled to the transceiver 35 and, typically, not coupled directly with any transducers present in the interface 14. As will be appreciated, the transceiver 35 may be any suitable transceiver capable of bi-directional communication through serial or parallel communication strategies. The local microprocessor 33 will be programmed to execute computer instructions locally such that a computing burden is removed from the computer 16. For example, positional information generated by the transducers may be processed locally by the local microprocessor 33, which in turn can send absolute position and velocity information to the computer 16. Still further, the local microprocessor 33 is capable of receiving incoming force commands from the computer 16, decoding such commands, and controlling the interface 14 accordingly. For more details, please see Rosenberg et al.'s U.S. Pat. No. 5,576,727.

In the perspective view of FIG. 2, the gimbal apparatus 25 of the present invention is illustrated in some detail. The gimbal apparatus 25 includes a support 34 and a gimbal mechanism 36 rotatably coupled to the support. The gimbal mechanism 36 preferably includes a U shaped base portion 38 including a base 40 and a pair of substantially parallel legs 42a and 42b extending upwardly therefrom. As used herein, "substantially parallel" will mean that two objects or axis are exactly or almost parallel, i.e. are at least within five or ten degrees of parallel, and are preferably within less than one degree of parallel. Similarly, the term "substantially perpendicular" will mean that two objects or axis are exactly or almost perpendicular, i.e. at least within five degrees or ten degrees of perpendicular, or more preferably within less than one degree of perpendicular.

The gimbal mechanism 36 also includes an elongated object (shaft) receiving portion 44 provided with an aperture 46 which extends entirely through the object receiving portion. The aperture 46 defines an object axis A₀ for an elongated cylindrical object, such that the shaft portion 28 of the laparoscopic tool 18 of FIG. 1. The object receiving portion 44 is at least partially disposed between the legs 42a and 42b of the U shaped base portion, and is pivotally coupled thereto such as by a pair of pivots, one of which is shown as pivot 48a in leg 42a. Another pivot 48b (not shown) is provided in leg 42b.

The object receiving portion 44 also includes a translation interface 50 and a rotation interface 52. The object receiving portion 44 includes a bearing section 54, a translation sensor section 56, and a rotation sensor section 58. The bearing section 54 includes a mass of material provided with a cylindrical bore 60 forming a portion of the aperture 46. The translation sensor section 56 includes a pair of opposing wall surfaces 62a and 62b, each of which is provided with a cylindrical bore receptive to the cylindrical object and forming a part of the aperture 46 which extends through the object receiving portion. The translation sensor section 56 includes a pair of opposing wall surfaces 64a and 64b of a wall 63 and which are provided with cylindrical bores receptive to the cylindrical object and therefore also forming a part of the aperture 46. In consequence, when an elongated cylindrical object is inserted into the object receiving portion 44 along axis A₀ it engages the bore 60 of the bearing section 54, and extends through bores provided in the surfaces 62a, 62b, 64a, and 64b to extend completely through the object receiving portion 44 along the aperture 46. In another embodiment of the present invention, wall 63 (and therefore wall surfaces 64a and 64b) is eliminated as being superfluous.

Referring briefly to FIG. 2a, an alternative construction for the translation interface 50 of FIG. 2 is shown at 50'. This alternative translation interface 50' is well adapted for very thin shafts, wires, catheters, and the like. The problem encountered with the translation interface 50 is that, for example, wires and catheters are flexible and therefore do not engage well with a single friction wheel. Therefore, the translation interface 50' includes a drive wheel 65a that is coupled to a sensor and/or actuator, and an idler wheel 65b. The wire or catheter 67 is pinched between the drive wheel 65a and the idler wheel 65b so that there is good frictional engagement between the catheter 67 and the drive wheel 65a.

The object receiving portion 44 is preferably a unitary mass of material made from aluminum or some other lightweight material such as a plastic. The object receiving portion 44 is preferably cast, molded, and/or machined as a monoblock member having the aforementioned bearing section, translation sensory section, and rotation sensory section. The materials and construction of U shaped base portion 38 preferably match the materials and construction techniques used for the production of object receiving portion 44.

The gimbal apparatus 25 illustrated in FIG. 2 constrains an object that is engaged with the object receiving portion 44 to four degrees of freedom. This is accomplished by allowing the U shaped base portion 38 to rotate around an axis A₁ relative to the support 34, by allowing the object receiving portion 44 to rotate around an axis A₂ relative to the U shaped base portion 38, by allowing the object to translate as illustrated by the arrow t along axis A₀ of aperture 46, and by allowing the object to rotate as indicated by arrow r around the axis A₀ of aperture 46.

Four electromechanical transducers are used in association with these four degrees of freedom. More particularly, a first degree of freedom electromechanical transducer 66 is arranged to transduce motion and/or force between the U shaped base portion 38 and the support 34, a second degree of freedom electromechanical transducer 68 is arranged to transduce motion and/or force between the U shaped base portion 38 and the object receiving portion 44, a third degree of freedom electromechanical transducer 70 is arranged to transduce motion and/or force between the object receiving portion 44 and an object engaged with the object receiving portion 44, and a fourth degree of freedom transducer 72 is arranged to transduce motion and/or force between the object receiving portion 44 and an object engaged with the object receiving portion 44.

By "associated with", "related to", or the like, it is meant that the electromechanical transducer is influenced by or influences one of the four degrees of freedom. The electromechanical transducers can be input transducers, in which case they sense motion along a respective degree of freedom and produce an electrical signal corresponding thereto for input into computer 16. Alternatively, the electromechanical transducers can be output transducers which receive electrical signals from computer 16 that cause the transducers to impart a force on the object in accordance with their respective degrees of freedom. The electromechanical transducers can also be hybrid or bi-directional transducers which operate both as sensors and as actuator devices.

A variety of transducers, readily available in the commercial market are suitable for use in the present invention. For example, if the transducers are input transducers ("sensors"), such sensors can include encoded wheel transducers, potentiometers, etc. Output transducers ("actuators") include stepper motors, servo motors, magnetic particle brakes, friction brakes, pneumatic actuators, etc. Hybrid or bi-directional transducers often pair input and output transducers together, but may also include a purely bi-directional transducer such as a permanent magnet electric motor/generator.

It should be noted that the present invention can utilize both absolute and relative sensors. An absolute sensor is one which the angle of the sensor is known in absolute terms, such as with an analog potentiometer. Relative sensors only provide relative angle information, and thus require some form of calibration step which provide a reference position for the relative angle information. The sensors described herein are primarily relative sensors. In consequence, there is an implied calibration step after system power-up wherein the shaft is placed in a known position within the gimbal mechanism and a calibration signal is provided to the system to provide the reference position mentioned above. All angles provided by the sensors are thereafter relative to that reference position. Such calibration methods are well known to those skilled in the art and, therefore, will not be discussed in any great detail herein.

A preferred input transducer for use of the present invention is an optical encoder model SI marketed by U.S. Digital of Vancouver, Wash. This transducer is an encoded wheel type input transducer. A preferred output transducer for use of the present invention is a d.c. motor model 2434.970-50 produced by Maxon of Fall River, Mass. This type of transducer is a servo motor type output transducer.

There a number of ways of attaching the transducers to the various members of the gimbal apparatus 25. In this preferred embodiment, a housing of transducer 66 is attached to the U shaped base portion 38, and a shaft of the transducer extends through an oversize bore (not shown) in base 40 to engage a press-fit bore (also not shown) in support 34. Therefore, rotation of the U shaped base portion 38 around axis A₁ will cause a rotation of a shaft of transducer 66. A housing of transducer 68 is attached to leg 42a of the U shaped base portion 38 such that its shaft forms pivot 48a. Therefore rotation of the object receiving portion 44 around axis A₂ will cause a rotation of the shaft of a second transducer. 68. The transducer 70 is attached to object receiving portion 44 and extends through a bore (not shown) in a wall 74 of the translation sensor section 56. The shaft 76 provides an axis about which the translation interface 50 can rotate. The fourth transducer 74 is attached to a wall 78 of rotation sensor section 58 and extends through a bore 80 in that wall 78. The shaft 82 of the transducer 72 engages a circumferential surface of rotation interface 52 and rotates therewith.

Axes A₁ and A₂ are substantially mutually perpendicular and intersect at an origin point O within object receiving portion 44. Axis A₀ also intersects this origin O. Shaft 76 rotates around an axis A₃ which is substantially perpendicular to the axis A₀. Shaft 58 of transducer 72 rotates around an axis A₄ which is substantially parallel to the axis A₀.

In FIG. 3, a front view of the gimbal apparatus 25 is used to illustrate one of the degrees of motion of the laparoscopic tool 18. The illustrated degree of freedom is the fourth degree of freedom, i.e. rotation around axis A₀ as illustrated by the arrow r in FIG. 2. This degree of freedom is detected by transducer 72. In this fourth degree of motion, the handle portion 26 of the laparoscopic tool 18 can rotate in a clockwise direction as indicated at 26' and in a counter clockwise direction as indicated at 26". Of course, the handle 26 can rotate a full 360° although this would require the release and re-grasping of the handle 26.

In FIG. 4, a second degree of freedom is illustrated. With this degree of freedom, the laparoscopic tool 18 can pivot upwardly as illustrated at 18' or downwardly (not shown). This rotation around A₂ is detected by transducer 68. It should be noted in the present embodiment, the laparoscopic tool 18 cannot rotate 360° around the axis A₂ because it is physically constrained by the support 34, portions of the gimbal mechanism 36, etc. However, in the present embodiment, the laparoscopic tool can achieve approximately 170 degrees of rotation around axis A₂.

FIG. 5 is top view of the gimbal apparatus 25 and illustrates the first and third degrees of freedom. The first degree of freedom is detected by transducer 66 as the laparoscopic tool 18 is pivoted or rotated around axis A₁ as illustrated at 18a and 18b. The third degree of freedom is detected by transducer 70 as the shaft portion 28 of laparoscopic tool 18 is moved back and fourth as illustrated by the arrow "t." This causes a rotation of translation interface 50 and the shaft 76 of the third transducer 70.

The four degrees of freedom are illustrated graphically in FIG. 6. The cylinder 66' represents the first transducer 66 and allows a first degree of freedom labeled "1st" around axis A₁. Cylinder 68' represents the sensor 68 and allows a second degree of freedom labeled "2nd" around axis A₂. Telescoping members 70a' and 70b' represent the third sensor 70 can sense movement along a third degree of freedom labeled "3rd" along axis A₀. Finally, a cylinder 72' attached to member 70b' represents the fourth transducer 72 and senses a fourth degree of freedom labeled "4th" around axis A₀. A member 84 is provided to indicate position and rotational direction relative to axis A₀.

In FIG. 7, a preferred input transducer (sensor) of the present invention is disclosed. Again, an input transducer of this type can be purchased as sensor model SI from U.S. Digital of Vancouver, Wash. The input transducer 86 includes a bearing block 88 having a bearing 89, a rotary shaft 90 supported by the bearing 89, and a sensing wheel 92 supported for rotation by shaft 90. The sensing wheel is preferably made from a clear, plastic material and is provided with a number of dark radial bands 94 near its circumference, such as by printing or silk screening. A first photodetector pair 96a including a light source 98a and a detector 100a are positioned on opposing sides of the sensing wheel 92 in alignment with the bands 94. Similarly, a second photodetector pair 96b including a light source 98b and a detector 100b are positioned on opposing sides of the sensing wheel 92 in alignment with the bands 94. As the sensing wheel 92 rotates as illustrated at 102 around an axis A, the bands 94 alternatively allow light emanating from light sources 98a and 98b to impinge or not impinge upon the detectors 100a and 100b, respectively. The electronic interface 14, coupled to the photodetector pairs 96a and 96b by cable 30, counts the bands 94 as they pass the photodetector pairs 96a and 96b to provide a signal on cable 32 to the computer 16 indicating the rotational position of the shaft 90 around axis A. The two pairs 96a and 96b are provided to determine the direction of rotation, as is well known to those skilled in the art of sensor design.

FIGS. 8 and 8a illustrate a modified laparoscopic tool 104. More particularly, a sensor 106 has been added to determine when the handle 108 has been squeezed, and the shaft 110 has been grooved or slotted for a purpose to be discussed subsequently. The sensor 106 can be coupled to the computer 16 through electronic interface 14 to provide additional input to the virtual reality system.

With reference to FIG. 8a, the shaft 110 is preferably hollow, having an axial bore 112 which aligns with axis A₀, and is provided with an elongated groove 114 which is parallel to an axis A_(L) of the shaft 110. This elongated groove 114 can be produced by any process including extruding the shaft 110 in the appropriate shape, or cutting the groove 114 with a machine tool, etc.

FIGS. 9 and 9a illustrate an alternate embodiment for transducer 72 which utilizes the shaft 110 and a detector mechanism similar to the one illustrated in FIG. 7. More particularly, the transducer 72' includes a sleeve 115 which is slidingly engaged with shaft 110. As seen in the cross sectional view of FIG. 9a, the sleeve 115 is a substantially cylindrical object having a central bore 116 which engages the circumference 118 of the shaft 110. The sleeve 115 has a key 120 which engages the slot 114 of the shaft 110. Therefore, while the sleeve can slide back and forth along the axis A_(L) as indicated at 122, but the sleeve 115 rotates with the shaft 110 as indicated at 124 due to the engagement of the key 120 with the groove 114. A sensing wheel 92' is affixed to a circumferential portion of sleeve 115 so that it rotates coaxially with the sleeve 115. A photodetector pair 96' senses the motion of bands 94' and produces an electrical signal on cable 30. The advantage of the embodiment shown in FIG. 9 and 9a is that rotation of the shaft around axis A_(L) is detected without the possibility of slippage. Another advantage of this embodiment is that it is more compact in design.

In FIG. 9b an alternate embodiment for a rotation interface 52' is shown. This alternate embodiment is well adapted for flexible shafts, wires, catheters and the like, such as the aforementioned catheter 67. The rotation interface 52' includes a transducer 72"" that is provided with a resilient grommet 73 having a hole that engages a circumferential portion of the catheter 67. The grommet 73 is preferably a rubber or plastic grommet that causes the catheter 67 to rotate coaxially as the catheter spins or rotates. Preferably, the mass of the transducer 72"" is kept very small so that it only takes a small amount of friction to ensure coaxial rotation of the catheter and transducer without slippage. Because the level of friction is so small, it does not substantially impede translational motion (i.e. in-out motion) of the catheter.

FIGS. 10 and 10a illustrate another embodiment 72" for the transducer 72 of FIG. 2. This embodiment has a number of points of similarity with the embodiment discussed with reference to FIGS. 9 and 9a, and it will be appreciated that elements with like reference numerals operate in a similar fashion. However, the embodiment of FIGS. 10 and 10a include a sheave 126 affixed to the circumference of sleeve 115 in the place of the sensing wheel 92' of FIG. 9 and FIG. 9a. A position sensor 128 has a shaft 130 which is coupled to the sheave 126 by a belt 132. The belt 132 can be any continuous loop structure including a resilient, rubber-type belt, a drive-chain type belt, etc. The shaft 130 of position sensor 128 therefore rotates with the sheave 126. The advantage of using a belt 132 or the like is that a substantial amount of force may be applied to the belt to, again, minimize slippage.

Another embodiment 72'" for the fourth transducer is illustrated in FIGS. 11 and 11a. Again, there are a number of points of similarity between the embodiments of FIGS. 11 and 11a and the previously described embodiments of FIGS. 9 and 9a and FIGS. 10 and 10a. Therefore, like reference numerals will again refer to like elements. In this embodiment, a sensor 134 has a shaft 136 which serves as the axle of a friction wheel 138 which, in turn, engages a circumferential surface of sleeve 115. Therefore, a rotation of the shaft 110 will cause a rotation of the sleeve 115, which will cause a rotation of the wheel 138 and the shaft 136 to create an electrical signal on cable 30.

With reference to all of the figures, and with particular reference to FIGS. 1 and 2, the shaft 28 of a laparoscopic tool 18 is inserted into aperture 46 along axis A₀, causing the shaft 28 to frictionally engage the translation interface (wheel) 50. In this instance, the translational interface 50 is a friction wheel made out of a rubber-like material. The shaft 28 is also in engagement with the rotation interface 52 which, in the embodiment of FIG. 2, is also a friction wheel made out of a rubber-like material. Rotation of the shaft 28 around the axis A₀ as illustrated by the arrow r will cause a rotation of the friction wheel 50 and therefore the shaft 82 of the sensor 72. A translation of the shaft 28 along axis A₀ will cause a rotation of the friction wheel 50 which rotates the shaft 76 of the transducer 70. A movement up or down of the laparoscopic tool 18 will cause a rotation of the shaft (pivot) 48a of transducer 68, and a side-to-side pivoting of the laparoscopic tool 18 will cause a rotational around axis A₁ which is detected by transducer 66.

To this point, the majority of the discussion has been under the assumption that the transducers are input transducers, i.e. the human/computer interface device is used an input device to the computer 16. However, it is also been mentioned that the interface device 12 can serve as an output device for the computer 16. When used as an output device, output transducers ("actuators") are used to respond to electrical signals developed by the computer 16 to impart a force upon the shaft 28 of the laparoscopic tool 18. This can provide useful movement and force (haptic) feedback to the doctor/trainee or other user. For example, if the laparoscopic tool encounters dense mass of tissue or a bone in the "virtual" patient, a force can be generated by transducer 70 making it harder for the doctor/trainee to push the shaft 28 further into the gimbal apparatus 25. Likewise, twisting motions can be imparted on the shaft 28 when the shaft encounters an obstacle within the virtual patient.

It should be noted that force applied to the shaft may not result in any movement of the shaft. This is because the shaft may be inhibited from movement by the hand of the operator who is grasping a handle or grip portion of the shaft. However, the force applied to the shaft may be sensed by the operator as haptic feedback.

With reference to FIG. 2, a method for mechanically interfacing an elongated mechanical object with an electrical system in accordance with the present invention includes first step of defining an origin in 3-dimensional space. This corresponds to the origin O at the intersection of axis A₁ and A₂. A second step is to physically constrain an elongated object in the 3-dimensional space such that a portion of the object always intersects the origin O and such that a portion of the object extending from the origin O defines a radius in a spherical coordinate system. The elongated object (such as shaft 28 of laparoscopic tool 18) is physically constrained in a 3-dimensional space by the aperture 46 of the object receiving portion 44. The portion of the shaft 28 extending from origin O defines the radius. A third step includes transducing a first electrical signal related to a first angular coordinate of the radius with a first transducer. This corresponds to the operation of transducer 66 which transduces a first electrical signal related to a first angular coordinate of the radius. A fourth step is transducing a second electrical signal related to a second angular coordinate of the radius. This corresponds to the operation of transducer 68 which transduces a second electrical signal. A fifth step is to transduce a third electrical signal related to the length of the radius, which corresponds to the operation of transducer 70. A sixth and final step is to electrically couple the transducers to an electrical system which, in this instance, is preferably a computer 16. An additional, optional step transduces a fourth electrical signal related to a rotation of the object around an object axis which intersects the origin O. This step corresponds to the operation of transducer 72. The transducers can be input transducers, output transducers, or bi-directional transducers.

It will be noted that the electrical system most frequently described in the present invention is a digital processing system or a computer. However, other digital systems, analog systems, and simple electric or electromechanical system can also be utilized with the apparatus and method of the present invention.

It will also be noted that while specific examples of "elongated objects" and "shafts" have been given, that these examples are not meant to be limiting. In general, equivalents of "elongated objects", "elongated cylindrical objects", "shafts", etc. include any object which can be grasped by a human operator to provide an interface between the operator and a computer system. By "grasp", it is meant that operators may releasably engage a grip portion of the object in some fashion, such as by hand, with their fingertips, or even orally in the case of handicapped persons. The "grip" can be a functional grip or handle attached to an elongated portion of the object, or can be a portion of the object itself, such as a portion of the length of a shaft that can be gripped and/or manipulated by the operator.

It should also be noted that flexible shafts, such as wires or catheters, do not always require three or four degrees of freedom. For example, if a human/computer interface for a catheter insertion virtual reality system is desired, only a translation interface (e.g. translation interface 50' of FIG. 2a) and rotation interface (such as rotation interface 52' of FIG. 9c) may be required. This is because a catheter can be moved in and out of a virtual patient (as sensed by translation interface 50') and can be twisted or rotated (as sensed by rotation interface 50'), but cannot be, in any practical manner, moved up or down or from side-to-side due to the flexibility of the catheter. In such applications, therefore, it is desirable to have a human/computer interface with only two degrees of freedom.

While this invention has been described in terms of several preferred embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. It is therefore intended that the following appended claims include all such alternatives, modifications, permutations and equivalents as fall within the true spirit and scope of the present invention. 

What is claimed is:
 1. A method for providing force feedback to a user of an interactive computer simulation, the method comprising:maintaining on a host computer having a display screen a virtual reality medical simulation suitable for representing a plurality of virtual reality objects within a graphical environment; coupling a human/computer interface with the host computer, the human/computer interface including at least a portion of a medical instrument suitable for manipulation by a user, an actuator arranged to generate force feedback to the user through the portion of the medical instrument in response to signals from the host computer, and a local microprocessor separate from the host computer and executing a local software routine at the same time as the maintaining of the virtual reality medical simulation by the host computer said local software routine operable to decode force commands transmitted from the host computer and related to the control of the actuator; representing the portion of the medical instrument as a virtual reality object within the virtual reality simulation, the virtual reality object having a simulated position corresponding to a position of the portion of the medical instrument; displaying on the display screen a graphical representation of the virtual reality simulation including a graphical object representing the portion of the medical instrument; detecting, at the human/computer interface, position information related to the portion of the medical instrument; transmitting position data from the human/computer interface to the host computer, the position data representing the position information related to the portion of the medical instrument; updating the virtual reality simulation such that the simulated position of the virtual reality object corresponds to the position data; receiving at the human/computer interface a force command from the host computer; and responding to the force command with the local microprocessor including decoding the force command and controlling said actuator in accordance with the force command thereby providing force feedback to the user, wherein said force feedback is provided in coordination with the updating of said virtual reality medical simulation, thereby creating a feel sensation that corresponds with the virtual reality object encountering a different virtual object in said virtual reality medical simulation.
 2. A method as recited in claim 1 wherein the human/computer interface further includes a gimbal mechanism and a support, the gimbal mechanism coupling the portion of the medical instrument to the support such that the portion of the medical instrument has at least two degrees of freedom of motion with respect to the support.
 3. A method as recited in claim 2 wherein the two degrees of freedom of motion are provided about a first axis and a second axis, the first and second axes being substantially mutually perpendicular and intersecting at an origin point.
 4. A method as recited in claim 3 wherein the human/computer interface further includes first and second sensors, the first sensor for detecting rotary motion of the portion of the medical instrument about the first axis and the second sensor for detecting rotary motion of the portion of the medical instrument about the second axis.
 5. A method as recited in claim 4 wherein the virtual reality simulation includes a representation of a body.
 6. A method as recited in claim 5 wherein the force feedback to the user includes a resistance force that causes a pushing of the portion of the medical instrument by the user more difficult.
 7. A method as recited in claim 6 wherein the portion of the medical instrument represents a laparoscopic instrument and is formed in the shape of a physical laparoscopic instrument handle.
 8. A method as recited in claim 5 wherein the medical instrument being represented is a catheter and the portion of the medical instrument is formed in the shape of a catheter wire.
 9. A method as recited in claim 6 wherein the force feedback to the user includes a twisting force on a shaft of the portion of the medical instrument when the virtual reality object encounters a virtual obstacle.
 10. A method as recited in claim 2 wherein the actuator is coupled between the support and the gimbal mechanism, the human/computer interface further including a continuous belt loop that is turned when the portion of the medical instrument is rotated by the user, the continuous loop belt arranged such that a substantial force may be applied to said continuous loop belt without causing substantial slippage of the continuous loop belt.
 11. A method as recited in claim 1 wherein the force command corresponds to the virtual reality object encountering an obstacle within the virtual reality medical simulation.
 12. A method as recited in claim 11 wherein the virtual reality object is a simulated surgical tool, the virtual reality medical simulation includes a simulated patient body, and the obstacle encountered by the virtual reality object involves the simulated surgical tool interacting with the simulated patient body.
 13. A method as recited in claim 1 wherein the actuator applies force through the portion of the medical instrument through the frictional engagement of a drive wheel.
 14. A method as recited in claim 4 wherein the portion of the medical instrument has a third linear degree of freedom, wherein force is applied to said third linear degree of freedom through frictional engagement of a drive wheel with said portion of the medical instrument.
 15. A virtual reality medical apparatus comprising:a host computer having display means; means for maintaining a virtual reality medical simulation on the host computer, the virtual reality medical simulation suitable for representing a plurality of virtual reality objects; human/computer interface means for providing force feedback to a user of the virtual reality apparatus, the human/computer interface means coupled with the host computer, the human/computer interface means including,a) at least a portion of a medical instrument suitable for manipulation by a user, b) actuator means arranged to generate force feedback to the user through the portion of the medical instrument in response to signals from the host computer, c) local microprocessor means separate from the host computer for executing a local software routine at the same time as the maintaining of the virtual reality medical simulation by the host computer the local software routine operable to decode force commands transmitted from the host computer in order to control the actuator such that the user experiences force sensations corresponding to interactions of virtual objects represented in the virtual reality medical simulation and in coordination with the maintaining of the virtual reality medical simulation, d) means for detecting position information related to the portion of the medical instrument, e) means for transmitting position data to the host computer, the position data representing the position information related to the portion of the medical instrument, and f) means for receiving a force command from the host computer; means for representing the portion of the medical instrument as a virtual reality object within the virtual reality medical simulation, the virtual reality object having a simulated position corresponding to a position of the portion of the medical instrument; means for displaying on the display means a graphical representation of the virtual reality medical simulation including a graphical object representing the portion of the medical instrument; and means for updating the virtual reality medical simulation such that the simulated position of the virtual reality object corresponds to the position data.
 16. A virtual reality apparatus as described in claim 15 wherein the human/computer interface means further includes gimbal means and support means, the gimbal means for coupling the portion of the medical instrument to the support means such that the portion of the medical instrument has at least two degrees of freedom of motion with respect to the support.
 17. A virtual reality apparatus as described in claim 16 wherein the two degrees of freedom of motion are provided about a first axis and a second axis, the first and second axes being substantially mutually perpendicular and intersecting at an origin point, the means for detecting position information including first and second sensor means, the first sensor means for detecting rotary motion of the portion of the medical instrument about the first axis and the second sensor means for detecting rotary motion of the portion of the medical instrument about the second axis.
 18. A virtual reality apparatus as described in claim 16 wherein the actuator means is coupled between the support means and the gimbal means, the human/computer interface means further including a continuous belt loop that is turned when the portion of the medical instrument is rotated by the user, the continuous loop belt arranged such that a substantial force may be applied to said continuous loop belt without causing substantial slippage of the continuous loop belt.
 19. A virtual reality apparatus as described in claim 15 wherein the virtual reality object represents a medical instrument and the virtual reality medical simulation is a representation of a body.
 20. A virtual reality apparatus as described in claim 15 wherein the force command corresponds to the virtual reality object encountering an obstacle within the virtual reality medical simulation. 